What is the difference between 115 and 124 grain 9mm FMJ. Is the 124 a "hotter" load. I always get the grains confused.

I don't think it's hotter. From what I've read, the 124gr load was the original bullet weight invented by Georg Luger. I'm not sure where or why the 115gr bullet was ever invented.

It doesn't have anything to do with how hot it is, just the weight of the bullet itself. The powder charge is what determines how hot a load will be. In those two grain weights you'll see standard pressure, +P, and +P+.

That is correct for a long long time from the P-08 Luger 124 gr. FMJ was the standard Military round for 9MM Parabellum. Today it is popularly called and even titled on the boxes
and advertised as 9MM Luger. Euro/Metric Desig .as 9x19. When Jacketed Hollow Points became into vogue in the late 1960s, Lee Juras at Super Vel made 9x19 in 90 or 100 gr. bullets with JHP and got greater velocity but they learned those shorter bullets may not feed - the big four of WIn.Rem. CCI & Federal came up with the 115 gr. JHPs to still get a bit more velocity and over the decades have come up with better more reliable expansion in JHPs.
There's also the factor of a 115 gr. vs 124 gr.
being shorter in length and thus a lower Ballistic Co-efficient - the higher the coefficcient the higher the retained velocity, also the higher mass also helps to retain velocity for penetration.

You can usually find less expensive FMJ bullets vs JHPS and both fire at the same velocity for about the same Point of Aim/Point of IMpact, so use the FMJs for practice, and the JHPs for ahem non-practice/HD/SD.

147 gr. are a controversial subject - some like the fact they are loaded to less than the speed of sound for less noise/muzzle blast, but
some think the 1000 fps limit penetration and performance but don't wouldn't 147 gr. bullets be designed to expand at the lower velocities?

Food for thought anyway.

R-

Grain is a unit of measurment (weight). There are 7000 grains in a pound.

quote:

Originally posted by Centenniel:
Grain is a unit of measurment (weight). There are 7000 grains in a pound.

...and as used in the original question, the 115 grain and 124 grain figures only pertain the the bullet weight... not the propellant weight. The 124gr may or may not be hotter (or vice-versa).

Given that the grain is the bullet weight and does not describe the powder charge, how can you tell from the ammo box how "hot" the ammo is? I in particular would wish to be able to identify low pressure .308 Winchester to fire in 7.62 military surplus rifles.

Grain is 190 Proof, which is 95% ethanol. Oh, wait, wrong thread...

All the ammo makers list their loadings and the velocities they get from testing them. All factory ammo is loaded to SAAMI specs, or is noted otherwise as some of the smaller manufactures do. If you want more information about a particular loading, I suggest contacting the maker directly.

No practical difference.

But we shooters like to worry our ammo like old dogs on a bone, so the makers oblige.

quote:

Originally posted by HOUSTON RICK:
Given that the grain is the bullet weight and does not describe the powder charge, how can you tell from the ammo box how "hot" the ammo is? I in particular would wish to be able to identify low pressure .308 Winchester to fire in 7.62 military surplus rifles.

You can't unless it is a special line of low pressure ammo.

The manufacturers stay within SAAMI limits, but they don't always even use the same powder for the next batch.

Time for you to learn to reload, so you can load to your liking.

I made a facetious response above, for which I apologize. (But do not retract. ) A grain is a unit of measurement of weight, as stated by others above. 7000 grains per avoirdupois pound.

OKFC is right; you should learn to reload, but first, buy yourself one of the latest editions of the major loading manuals, from Speer, Sierra, Hornady, Norma, Lyman, or better yet, buy 2 or 3 of them. Before you even buy a piece of loading equipment or any components, read the manual(s). You'll be glad you did!

quote:

Originally posted by 38-44HD45:
I made a facetious response above, for which I apologize. (But do not retract. ) A grain is a unit of measurement of weight, as stated by others above. 7000 grains per avoirdupois pound.

OKFC is right; you should learn to reload, but first, buy yourself one of the latest editions of the major loading manuals, from Speer, Sierra, Hornady, Norma, Lyman, or better yet, buy 2 or 3 of them. Before you even buy a piece of loading equipment or any components, read the manual(s). You'll be glad you did!

Right on!!!